 We need to find the area of this triangle, but we don't know the height so we cannot use this formula But we know the sides of the triangle so we will use this formula, which is also called as Heron's formula But this S is alone What if we had an S-D to give it company just like the others in fact we do I'm going to draw a circle and inside this circle I'm going to draw a Quadrilateral if the side lengths are A, B, C and D and this quadrilateral is not a rectangle or a square Then I can't find the area by using A equal to C into D because that only works for Rectangles and squares Instead what I can do is use the Coordinational version of Heron's formula which says A is equal to under root S minus A into S minus B into S minus C into S minus D